- Email: [email protected]
The Role of India-Asia Collision in the Amalgamation of the Gondwana-derived Blocks and Deep-seated Magmatism During the Paleogene at the Himalayan Foreland Basin and Around the Gongha Syntaxis in the South China Block
Gondwana Research, V. 2, No. 4, p p . 510-512.
GR
01999 International Assocriifionfor Gondrvana Reseorch, Japan. ISSN: 1342-937X
Goizdwaiza Research
The Role of India-Asia Collision in the Amalgamation of the Gondwana-derived Blocks and Deep-seated Magmatism During the Paleogene at the Himalayan Foreland Basin and Around the Gongha Syntaxis in the South China Block S.K.Acharyya Geological Survey of India, Calcutta 700016, India, e-mail: [email protected]
Continental blocks were rifted out in phases from the northern margin of the East Gondwanic Indo-Aus tralian continent during Paleo-Mesozoic. The South China and Indochina blocks possibly rifted during early Palaeozoic, whereas the Tibetan and Sibumasu blocks rifted during Permo-Carboniferous when the said margin was under glacial and/or cool climatic condition. The latter blocks drifted northward to warmer position during mid-late Permian. The Palaeo-Tethys located to the north of these blocks closed during late Permian-Triassic as these blocks were accreted to the South C h n a and Indochina blocks now forming parts of Asia. The Indo-Burma-Andaman (IBA block of Acharyya, 1996), Sikule, Lolotoi blocks (presently located in central Sumatra) were also rifted from the same Indo-Australian margin but during late Jurassic, followed by break-up of the Indian and the Australian continents during early Cretaceous initiating opening of the Indian Ocean. The Neo-Tethys separating Indian and Tibetan blocks expanded during major parts of the Mesozoic, however, the opening of the Indian Ocean was phased with closing of the poly-islandic Tethyan Ocean. The Palaeo and NeoTethyan sutures in Tibet, Yunnan, Laos-Thailand and Vietnam (Fig.l) reveal the complex opening and closing history of the Tethys. The IBA block appears to have rotated clockwise from its earlier E-W orientation because of 90"E and adjacent dextral transcurrent fault movements resulting in faster northward movement of the Indian plate relative to the Australian plate during late Cretaceous-early Eocene. IndiaTibet terminal collision during early-middle Eocene was a mega tectonic event. The Himalayan orogeny and the eastward strike-slip extrusion of the Indochina block of the
Southeast Asian continental collage along the Ailao Shan Red River shear zone have long been recognised as the two most spectacular results of India-Asia collision. Recent studies have identified discontinuous occurrences of earlymid Eocene volcanics with continental-flood-basalt (Table1) and other affinities along the entire length of the Himalayan foreland basin (Fig. 1 inset) (Acharyya, 1998a, b). These volcanics are thus broadly coeval with the terminal collision that occurred along a site located further north. Late Paleogene (ca. 30-40 Ma) ultra potassic mafic magmatism also occurred at the marginal parts of the South China block, around the Gongha syntaxis (Fig. 1)located along the outer oroclinal bend opposite Namche-Barwa syntaxis. These were soon after displaced along the Ailao Shan shear zone (Chung et al., 1997).The CFB-type Eocene foreland volcanism from the Himalayan belt, contemporaneous to terminal collision, followed by the late Paleogene highly potassic magmatism around the Gongha syntaxis, have been inferred to be genetically related to the process of India-Asia continental collision (Acharyya, 1999). The nature and chemistry of both groups of magmas indicate their generation by similar petrogenetic and tectonic processes. Their site-specific location and time sequence further link them genetically to the India-Asia collision process a n d Indian continent's indentation-induced syntaxial buckling at the marginal parts of the South China continent located opposite Assam-Namche-Barwa syntaxis. Deep mantle-reaching fractures were apparently produced during terminal collision at the flexed leading edge of the Indian continent, and later in time at the outer oroclinalbend of the marginal parts of South China continent, generating typical magma.
51 1
Table 1. Composition of Eocene volcanics from the I-Iimalayan foreland basin. Abor Volcanics, Siang window and adjacent areas
Dwar-khola Volcanics, Central Nepal foothills
Peontra Volcanics, Deoban window
49.73 - 55.40 (45.98-51.07)
44.96 - 49.62 (one sample of ultrabasic composition - 38.97) 5.16 - 7.24 0.02 - 0.73 4.21 - 4.92 1.03 - 1.28 12.43 - 13.77 2.06 - 2.66 1.34 - 2.11 6447 - 7730
51.46 - 52.77
6.3 - 11.48 (5.95 - 9.25) 0.07 - 0.48 (0.31-2.06) 2.6 - 4.4 (6.3 - 20.8) 0.94 - 1.13* 9.1 - 12.1 (8.0 - 10.4) 1.75 - 2.82 (0.63- 1.27) 0.9 - 1.36 * 2745 - 4425 *
7.0 - 9.58 0.68 - 0.85 No data
Values for alkaline members from the Abor volcanics shown in parenthesis, total common range shown with *, location of volcanics shown in Fig.] 3so
3oo
25’
2oo
15’
Fig.1.
Sketch map of a part of Southeast Asia. Main Suture/Thrust/Fault (number in parenthesis refers to elements in Inset map): ASRR (5)- Ailao Shan Red River shear zone, BNS (2)- Bangong Nujiang Suture, CMS (4)- Changning-Menglian Suture, ITS (1)-Indus Tsangpo Suture, JS (3)Jingshajiang Suture, LMS- Lungmen Shan Thrust, MBT- Main Boundary Thrust, SF- Shan Fault, SMS- Song Ma Suture, UNS(4)- Uttaradit Nan Suture, B- Bengal Basin, SL- Shillong Massif, AS- Assam Shelf, IBR- Indo-Burma Range. Locations of Himalayan foreland volcanism: 5- Siang window, T-Tipi, and those in inset map: D-Dwar-khola, P- Peontra, K- Kanthan; Syntaxes A- Assam, G- Gongha, H- KashmirHazara (Inset map), N- Namchc-Barwa; Blocks: C- Changtang, IC- Indochina, IB- Indoburma, 5- Sibumasu, SC- South China, NC- North China.
The ophiolite train exposed in the Indo-Burma Range and Andaman Islands does not represent the eastern suture of the Indian plate. The Mesozoic-early Eocene ophiolites, their Mid Eocene cover and contemporaneous but tectonically underlying subduction-related trench sediments occur instead as klippe on IBA (Figl), caused due to late Oligocene oblique collision between the SIBUMASU and IBA. The suture is located in Central Burma - Sumatra. A subduction zone, N-Q magmatic arc and back-arc opening had developed along the western margin and east of IBA respectively, due to oblique convergence between the IBA and Indian plate. The NE prolongation of the Indian Gondwana Research, V. 2,No. 4, 1999
continent collided against the northern end of IBA during Mio-Pliocene, causing upliftment and overthrusting of the Shllong massif over the Bengal Basin located over its passive margin to the south (Fig.l), whereas, the Eocene distal shelf sediments of IBA were overthrusted over the Tertiary cover of the Assam shelf.
References Acharyya, S.K. (1996)Accretion of Indo-Australian Gondwanic blocks along peri-Indian collision margins. In : Gondwana Nine, gtll Int. Gondwana Symp. Hyderabad, 1994, India, Oxford IBH, New Delhi, pp.1029-1049.
512
Acharyya, S.K. (1998a) Break-up of the Greater Indo-Australian continent and accretion of blocks framing South and East Asia. J. Geodynamics, v.26, pp. 149-170. Acharyya, S.K. (199810) Foreland Palaeogene rocks of the Eastern Himalaya: their basin extension, magmatism and tectonics. In: Proc.Workshop, Himalayan foreland basin with special reference to pre-Siwalik Tertiaries, Jammu Univ., Jammu, March 1998, Wadia Inst.Him.Geol., Abstr., pp. 1-2.
Acharyya, S.K.(1999) India-Asia collision and its relation to deep-seated Paleogene magmatism in Himalayan foreland basin, and around the Gongha syntaxis (submitted to Terra
Nova). Chung Sunlin, Lo, C., Wang, I?, Chen, C., Yem, N.T. and Wu, G. (1997) Intraplate extension prior to continental extrusion along the Ailao Shan-Red River shear zone. Geology, v.25, pp.311-314.
Gondiuana Research, V. 2, No. 4, p p . 512-515. 01999 International Association for Gondwana Research, lapan. ISSN: 1342-937X
GR
Gondwnrza Research
The Geotectonic Character of SE Asia and Cenozoic Tectonic History of South China Sea Yao Bochu Gtiangzhou Marine Geological Survey, Gziangzhou 510075, China
SE Asia area is one of the tectonically complex areas in the world. It consists of several micro-plates derived from the northern margin of Gondwanaland, including many arcs and accretionary prisms, w h c h finally collided and sutured together through a series of tectonic movements from Paleozoic to Cenozoic. The Indochina block is located in the Northwest margin of the South China Sea. Gatinsky and Hutchson (1986) subdivided it into four micro blocks: Sinnburmalaya, Phu Hoat, Indosinia and East Malay. Hagashi (1989)subdivided it as three micro blocks: Shag Thai, Kan Tum, and South China separated by the NE-SW striking Red River fault zone (Song Ma and Song Da suture zones) and NNE-SSW trending Dien Bien Phu fault zone (Uttaradit suture zone) according to Landsat data (Fig. 1).The Shag Thai and Kan Tum blocks have sutured in the Permian and formed the Indochina block (Bunopas and Vella, 1978; Ridd, 1990). In the Triassic, the Indochina block and South China block have collided and sutured together along the Song Ma and Song Da zone (Hutchson, 1975). The Borneo Island is situated in the southern margin of South China Sea. The Lupar fault zone and its continuation has partly broken the island into two areas: southwest Borneo and north Borneo. The basement of southwest Borneo consists of Paleozoic and Mesozoic igneous rocks,
sedimentary rocks and metamorphic rocks. The oldest rock here is the crystalline schist with an age of 320-201 Ma (Hutchson, 1984, 1986). The north Borneo is a Cenozoic accretionary prism (Jacobson,1970; Lee and Mc Cate, 1986). The Rajang formation (late Cretaceous to early Eocene) is distributed in the southern area, and the Crocker formation (Eocene to Oligocene) is distributed in the northern area (Hall, 1997). The oldest rocks of Palawan Island are schist, phyllite, slate and quartzite. In northeast Palawan, these rocks overlie middle Triassic sandstone, tuff and slate (Hutchson, 1973). In Mindoro, the basement is Triassic schist and slate. The southern part of the Ulugan fault in Palawan island exposes an ophiolite arc, consisting of ophiolite and greenschist (Rangin, 1985; Hutchson, 1975; Faure, 1989). Hinz and Schluter (1985) believe that this ophiolite terrane is an allochthon thrusted from southeast to northwest. The Philippine Islands are constituted of ophiolite and Mesozoic and Tertiary arcs. In the eastern part is the Philippine trench, the Philippine sea plate is subducting westward along this trench. The Philippine Islands is a volcanic arc of the subduction zone. In the western part of the islands, the South China Sea plate is subducting eastward along the Manila trench. Paleomagnetic data show that in the Tertiary, the rotation history of the Philippine
GR
01999 International Assocriifionfor Gondrvana Reseorch, Japan. ISSN: 1342-937X
Goizdwaiza Research
The Role of India-Asia Collision in the Amalgamation of the Gondwana-derived Blocks and Deep-seated Magmatism During the Paleogene at the Himalayan Foreland Basin and Around the Gongha Syntaxis in the South China Block S.K.Acharyya Geological Survey of India, Calcutta 700016, India, e-mail: [email protected]
Continental blocks were rifted out in phases from the northern margin of the East Gondwanic Indo-Aus tralian continent during Paleo-Mesozoic. The South China and Indochina blocks possibly rifted during early Palaeozoic, whereas the Tibetan and Sibumasu blocks rifted during Permo-Carboniferous when the said margin was under glacial and/or cool climatic condition. The latter blocks drifted northward to warmer position during mid-late Permian. The Palaeo-Tethys located to the north of these blocks closed during late Permian-Triassic as these blocks were accreted to the South C h n a and Indochina blocks now forming parts of Asia. The Indo-Burma-Andaman (IBA block of Acharyya, 1996), Sikule, Lolotoi blocks (presently located in central Sumatra) were also rifted from the same Indo-Australian margin but during late Jurassic, followed by break-up of the Indian and the Australian continents during early Cretaceous initiating opening of the Indian Ocean. The Neo-Tethys separating Indian and Tibetan blocks expanded during major parts of the Mesozoic, however, the opening of the Indian Ocean was phased with closing of the poly-islandic Tethyan Ocean. The Palaeo and NeoTethyan sutures in Tibet, Yunnan, Laos-Thailand and Vietnam (Fig.l) reveal the complex opening and closing history of the Tethys. The IBA block appears to have rotated clockwise from its earlier E-W orientation because of 90"E and adjacent dextral transcurrent fault movements resulting in faster northward movement of the Indian plate relative to the Australian plate during late Cretaceous-early Eocene. IndiaTibet terminal collision during early-middle Eocene was a mega tectonic event. The Himalayan orogeny and the eastward strike-slip extrusion of the Indochina block of the
Southeast Asian continental collage along the Ailao Shan Red River shear zone have long been recognised as the two most spectacular results of India-Asia collision. Recent studies have identified discontinuous occurrences of earlymid Eocene volcanics with continental-flood-basalt (Table1) and other affinities along the entire length of the Himalayan foreland basin (Fig. 1 inset) (Acharyya, 1998a, b). These volcanics are thus broadly coeval with the terminal collision that occurred along a site located further north. Late Paleogene (ca. 30-40 Ma) ultra potassic mafic magmatism also occurred at the marginal parts of the South China block, around the Gongha syntaxis (Fig. 1)located along the outer oroclinal bend opposite Namche-Barwa syntaxis. These were soon after displaced along the Ailao Shan shear zone (Chung et al., 1997).The CFB-type Eocene foreland volcanism from the Himalayan belt, contemporaneous to terminal collision, followed by the late Paleogene highly potassic magmatism around the Gongha syntaxis, have been inferred to be genetically related to the process of India-Asia continental collision (Acharyya, 1999). The nature and chemistry of both groups of magmas indicate their generation by similar petrogenetic and tectonic processes. Their site-specific location and time sequence further link them genetically to the India-Asia collision process a n d Indian continent's indentation-induced syntaxial buckling at the marginal parts of the South China continent located opposite Assam-Namche-Barwa syntaxis. Deep mantle-reaching fractures were apparently produced during terminal collision at the flexed leading edge of the Indian continent, and later in time at the outer oroclinalbend of the marginal parts of South China continent, generating typical magma.
51 1
Table 1. Composition of Eocene volcanics from the I-Iimalayan foreland basin. Abor Volcanics, Siang window and adjacent areas
Dwar-khola Volcanics, Central Nepal foothills
Peontra Volcanics, Deoban window
49.73 - 55.40 (45.98-51.07)
44.96 - 49.62 (one sample of ultrabasic composition - 38.97) 5.16 - 7.24 0.02 - 0.73 4.21 - 4.92 1.03 - 1.28 12.43 - 13.77 2.06 - 2.66 1.34 - 2.11 6447 - 7730
51.46 - 52.77
6.3 - 11.48 (5.95 - 9.25) 0.07 - 0.48 (0.31-2.06) 2.6 - 4.4 (6.3 - 20.8) 0.94 - 1.13* 9.1 - 12.1 (8.0 - 10.4) 1.75 - 2.82 (0.63- 1.27) 0.9 - 1.36 * 2745 - 4425 *
7.0 - 9.58 0.68 - 0.85 No data
Values for alkaline members from the Abor volcanics shown in parenthesis, total common range shown with *, location of volcanics shown in Fig.] 3so
3oo
25’
2oo
15’
Fig.1.
Sketch map of a part of Southeast Asia. Main Suture/Thrust/Fault (number in parenthesis refers to elements in Inset map): ASRR (5)- Ailao Shan Red River shear zone, BNS (2)- Bangong Nujiang Suture, CMS (4)- Changning-Menglian Suture, ITS (1)-Indus Tsangpo Suture, JS (3)Jingshajiang Suture, LMS- Lungmen Shan Thrust, MBT- Main Boundary Thrust, SF- Shan Fault, SMS- Song Ma Suture, UNS(4)- Uttaradit Nan Suture, B- Bengal Basin, SL- Shillong Massif, AS- Assam Shelf, IBR- Indo-Burma Range. Locations of Himalayan foreland volcanism: 5- Siang window, T-Tipi, and those in inset map: D-Dwar-khola, P- Peontra, K- Kanthan; Syntaxes A- Assam, G- Gongha, H- KashmirHazara (Inset map), N- Namchc-Barwa; Blocks: C- Changtang, IC- Indochina, IB- Indoburma, 5- Sibumasu, SC- South China, NC- North China.
The ophiolite train exposed in the Indo-Burma Range and Andaman Islands does not represent the eastern suture of the Indian plate. The Mesozoic-early Eocene ophiolites, their Mid Eocene cover and contemporaneous but tectonically underlying subduction-related trench sediments occur instead as klippe on IBA (Figl), caused due to late Oligocene oblique collision between the SIBUMASU and IBA. The suture is located in Central Burma - Sumatra. A subduction zone, N-Q magmatic arc and back-arc opening had developed along the western margin and east of IBA respectively, due to oblique convergence between the IBA and Indian plate. The NE prolongation of the Indian Gondwana Research, V. 2,No. 4, 1999
continent collided against the northern end of IBA during Mio-Pliocene, causing upliftment and overthrusting of the Shllong massif over the Bengal Basin located over its passive margin to the south (Fig.l), whereas, the Eocene distal shelf sediments of IBA were overthrusted over the Tertiary cover of the Assam shelf.
References Acharyya, S.K. (1996)Accretion of Indo-Australian Gondwanic blocks along peri-Indian collision margins. In : Gondwana Nine, gtll Int. Gondwana Symp. Hyderabad, 1994, India, Oxford IBH, New Delhi, pp.1029-1049.
512
Acharyya, S.K. (1998a) Break-up of the Greater Indo-Australian continent and accretion of blocks framing South and East Asia. J. Geodynamics, v.26, pp. 149-170. Acharyya, S.K. (199810) Foreland Palaeogene rocks of the Eastern Himalaya: their basin extension, magmatism and tectonics. In: Proc.Workshop, Himalayan foreland basin with special reference to pre-Siwalik Tertiaries, Jammu Univ., Jammu, March 1998, Wadia Inst.Him.Geol., Abstr., pp. 1-2.
Acharyya, S.K.(1999) India-Asia collision and its relation to deep-seated Paleogene magmatism in Himalayan foreland basin, and around the Gongha syntaxis (submitted to Terra
Nova). Chung Sunlin, Lo, C., Wang, I?, Chen, C., Yem, N.T. and Wu, G. (1997) Intraplate extension prior to continental extrusion along the Ailao Shan-Red River shear zone. Geology, v.25, pp.311-314.
Gondiuana Research, V. 2, No. 4, p p . 512-515. 01999 International Association for Gondwana Research, lapan. ISSN: 1342-937X
GR
Gondwnrza Research
The Geotectonic Character of SE Asia and Cenozoic Tectonic History of South China Sea Yao Bochu Gtiangzhou Marine Geological Survey, Gziangzhou 510075, China
SE Asia area is one of the tectonically complex areas in the world. It consists of several micro-plates derived from the northern margin of Gondwanaland, including many arcs and accretionary prisms, w h c h finally collided and sutured together through a series of tectonic movements from Paleozoic to Cenozoic. The Indochina block is located in the Northwest margin of the South China Sea. Gatinsky and Hutchson (1986) subdivided it into four micro blocks: Sinnburmalaya, Phu Hoat, Indosinia and East Malay. Hagashi (1989)subdivided it as three micro blocks: Shag Thai, Kan Tum, and South China separated by the NE-SW striking Red River fault zone (Song Ma and Song Da suture zones) and NNE-SSW trending Dien Bien Phu fault zone (Uttaradit suture zone) according to Landsat data (Fig. 1).The Shag Thai and Kan Tum blocks have sutured in the Permian and formed the Indochina block (Bunopas and Vella, 1978; Ridd, 1990). In the Triassic, the Indochina block and South China block have collided and sutured together along the Song Ma and Song Da zone (Hutchson, 1975). The Borneo Island is situated in the southern margin of South China Sea. The Lupar fault zone and its continuation has partly broken the island into two areas: southwest Borneo and north Borneo. The basement of southwest Borneo consists of Paleozoic and Mesozoic igneous rocks,
sedimentary rocks and metamorphic rocks. The oldest rock here is the crystalline schist with an age of 320-201 Ma (Hutchson, 1984, 1986). The north Borneo is a Cenozoic accretionary prism (Jacobson,1970; Lee and Mc Cate, 1986). The Rajang formation (late Cretaceous to early Eocene) is distributed in the southern area, and the Crocker formation (Eocene to Oligocene) is distributed in the northern area (Hall, 1997). The oldest rocks of Palawan Island are schist, phyllite, slate and quartzite. In northeast Palawan, these rocks overlie middle Triassic sandstone, tuff and slate (Hutchson, 1973). In Mindoro, the basement is Triassic schist and slate. The southern part of the Ulugan fault in Palawan island exposes an ophiolite arc, consisting of ophiolite and greenschist (Rangin, 1985; Hutchson, 1975; Faure, 1989). Hinz and Schluter (1985) believe that this ophiolite terrane is an allochthon thrusted from southeast to northwest. The Philippine Islands are constituted of ophiolite and Mesozoic and Tertiary arcs. In the eastern part is the Philippine trench, the Philippine sea plate is subducting westward along this trench. The Philippine Islands is a volcanic arc of the subduction zone. In the western part of the islands, the South China Sea plate is subducting eastward along the Manila trench. Paleomagnetic data show that in the Tertiary, the rotation history of the Philippine